(1) Field of the Invention
The present invention relates to a method of producing an air inlet in a multi-walled container particularly intended to contain a liquid or thick consistency product such as is often encountered in the pharmaceutical or cosmetics industry.
These containers are of the type consisting of a rigid outer casing, inside which is placed a flexible pocket intended to contain the product and in association with a withdrawal member without air inlet, usually a pump.
Such a container is obtained in a mold by a method of blow-molding coextrusion of a parison formed of a main outer layer made of relatively rigid plastic, and a secondary inner layer, made of relatively flexible plastic.
These layers do not stick together, so as to delaminate without difficulty, after the fusion by pinching of a zone of the inner layer, then the removal of the parison residue called a sprue thus formed when the blow-molding coextrusion method is used, and finally the creation of an air inlet between the flexible layer and the rigid layer of said parison.
Specifically, when the withdrawal member is actuated in the flexible inner pocket, this pocket collapses while leaving the rigid outer casing intact.
(2) Prior Art
In the known containers of this type, there is a large number of pieces: the pocket formed by the flexible inner layer, the rigid outer casing, the withdrawal member and an interface piece between the three components.
An interface piece must then be designed to allow a correct assembly between the withdrawal member and the pocket formed by the thin inner layer in order to give sufficient rigidity to the tip of said pocket and allow a tightening and a necessary seal so that there is no leak at the tip.
An assembly and fusions between the pocket and the intermediate interface piece are therefore necessary, which incurs an additional cost.
It is also known practice to create a withdrawal member that does not allow the inlet of air into the pocket formed by the thin inner layer.
It is also a known practice to create an air inlet means between the rigid outer casing and the pocket formed by the thin inner layer.
During the withdrawal and collapsing of the pocket formed by the thin inner layer, a pressure reduction is created between the rigid outer casing and the pocket formed by the thin inner layer. This pressure reduction risks causing the rigid outer casing to collapse. To remedy this problem, it is a known practice to create a hole either in the interface piece, or in the rigid outer casing so that the outside air passes through this hole and compensates for the pressure reduction.
It is also a known practice to create the two layers in question, that is to say the rigid outer casing and the flexible inner pocket, in a single operation by multi-layer, but not delaminate, extrusion.
It is also a known practice to create two layers that do not stick together. The layers must have the following properties:                rigid outer layer,        flexible inner layer that is deformable and inert relative to the content,        use of an intermediate material that ensures delamination,        where appropriate, a layer of barrier material coupled to the inner layer,        as an option, layers of bonding material or adhesive to bond the layers that must not delaminate.        
Equally, it is a known practice to make a hole that pierces the rigid outer casing without piercing the pocket formed by the thin inner layer by drilling or boring, but there is then a risk of piercing and/or weakening the pocket formed by the thin inner layer. It is therefore necessary to inspect all the pieces to verify that they are in good condition. In the case of an insufficiently deep drilling, the air inlet does not operate.
In the case of an over-deep drilling, the inner layer may then be pierced, or at least be weakened in the drilling zone.
It is also a known practice to initiate the delamination to make subsequent use easier but several disadvantages appear, such as: variation of the volume of the pocket formed by the thin inner layer; air hole zone that changes the capacity; complex inlet (aspirating the pocket formed by the thin inner layer and then blowing it out again), reducing the esthetics due to the crumpling of the zone of the pocket formed by the delaminated thin inner layer.